Overall, the objective of this project is to define the mechanism by which maternal estrogen progesterone control metabolism and development in preimplantation mouse embryos. The level of metabolism by normal and delayed implanting embryos in utero will be used to assay uterine fluid (as obtained by flushing the uterus) for inhibitory and/or stimulatory factors that may be involved in embryonic dormancy, and the subsequent activation as the prolonged free-living phase of delayed implantation is terminated. Once identified, inhibitory and/or stimulatory factors in uterine fluid will be characterized chemically. In addition, it will be determined whether or not substances such as enzymes and the inhibitors of enzymes, that have been identified in uterine fluid, are altered by the hormonal conditions of normal or delayed implantation. These substances will also be tested on embryos in vitro to determine whether or not they will mimic the pattern of metabolism characteristic of either normal or delayed implanting blastocysts. The techniques of egg transplantation, in vitro culture, column chromatography, scintillation counting and enzyme assay, electrophoresis, and autoradiography will be used in the proposed experiments. The potential significance of this research is that it may clarify the roles of the maternal organism, the endometrium and uterine fluid, and the blastocyst in implantation and thus not only add to our understanding of normal development, but also provide specific leads for 'interception' as a method of fertility control.